Currently a formula in Tableau can look plain and a bit boring:

I would suggest highlighting the syntax words like Case, When, Then, End etc. The result should look like this:

I would also add that we could highlight the quotes so that it becomes:

When 'California' Then 'CA'

Talking about visualization ... This will visualize the difference between user-input texts and Tableau-defined syntactic words. It will make formulae a lot easier to read and to debug.

Already submitted the idea as a feature request. If you like the idea, please upvote it! The more votes, the sooner it will be implemented.